The drive line coupling is well known throughout the automotive industry. In an active all-wheel drive system, the coupling is used to transfer torque from the engine to the wheels that are not normally driven except in certain circumstances, such as wheel slip in the primary drive wheels due to icy or rainy conditions. The traditional coupling for an all-wheel drive application uses a driveshaft to transfer torque from the transfer case to both the front and rear axle as needed, whereby either the front or rear axle is continuously engaged and the other axle is engaged by the operator or the vehicle's computer, as necessary.
A transfer case is generally attached to the transmission output shaft where it receives torque from the transmission. In an all-wheel drive system, torque is transferred to the appropriate axles by the transfer case. The primary drive wheels, those which are constantly driven, are driven by a differential placed between the transfer case and the primary drive wheels. The secondary drive wheels, those which are not constantly driven, are driven by a differential placed between the transfer case and the secondary drive wheels.
In an active all-wheel drive system, torque from the transmission is constantly being directed to both the primary and secondary drive axles via the transfer case. The active all-wheel drive system optimizes the traction of the vehicle by directing torque to the secondary drive wheels when a slip is detected in the primary drive wheels. The active all-wheel drive system uses a coupling at the secondary differential or integrated into the transfer case to control power distribution. The flow of torque to the secondary drive wheels can be controlled at either the transfer case or at the coupling of the secondary differential. If the torque is controlled at the secondary drive axle coupling, the transfer case is constantly directing torque to the primary and secondary drive wheels. If the torque is controlled by the transfer case, a secondary coupling is not necessary, as a direct system can be used at the differential due to the transfer case's additional control of the torque flow.
The current state of the art in an active all-wheel drive system uses a transfer case which constantly transfers torque to the secondary drive wheels through a coupling device. The coupling device contains an input flange which is coupled to an input shaft, which transfers torque to the output shaft upon the exertion of force on the clutch pack by a ball and ramp mechanism. The coupling system does not transfer the input torque to the wheels in the traditional non-slip mode. The ball and ramp mechanism is activated by the rotation of an electric motor which causes the ramps to expand. The expansion of the ramps compresses the clutch pack and connects the input shaft and the output shaft thereby transferring the torque from the input shaft to the output shaft and ultimately to the secondary drive wheels. The use of a ball and ramp mechanism creates a linear ratio and therefore is not fully optimized with respect to the speed in which torque is transferred or the size of the electric motor.
Thus, there is a need for an improved actuating drive line coupler.